This project builds on six years of participant-observation ethnographic fieldwork among middle-aged homeless heroin injectors. It examines the HIV and HCV risk implications of the growing phenomenon in the United States of prematurely geriatric substance abusers by examining the aging process among both young and older injectors. The entrance into our field site of a new network of injectors who are under 30 years-old provides a natural social laboratory to document comparatively the ways the aging process changes risk of blood-borne infections and co-morbid conditions. We are contributing to a socio-culturally contextualized understanding of variance in HIV and HCV infection rates among differentially vulnerable profiles of street based IDUs that is informed theoretically at the macro-structural level. The logics for risky injection and sexual practices are examined in their larger socio-cultural and pragmatic contexts, including: 1) poly-drug abuse; 2) income-generating strategies; 3) interface with services; 4) family relations; 5) status hierarchies; 6) gender and sexuality; 7) ethnicity/race; and 8) oppositional cultural identities. A cross-generational and multi gender ethnographic team will collect qualitative data inside the shooting/sleeping encampments and income generating territory of two overlapping social networks of injectors (core N= 25-40 at any given time; peripheral N=50-70). The project extends its ongoing collaboration with epidemiologists to clinical researchers and caregivers who work with comparable data sets of injectors in San Francisco in order to engage a multi-method dialogue. An immediate applied goal is to promote communication across the research/service interface. We will offer providers of health care, outreach and treatment an indigenous perspective on the effectiveness of their services among substance abusers by age cohort through our comparative study of: 1) injectors from the baby boom generation who are advancing from mid-life to old age with rapidly deteriorating health and ongoing HIV risk; and 2) homeless youth injectors (many of whom are the children of middle-aged substance abusers) who engage in risky injection and sexual practices.